R438a is otherwise known as MO99. It is a medium and low temperature application refrigerant that is compatible with *SOME* R22 Freon parts and pieces when used with the proper application.

It is not compatible with high temp application appliance like air conditioning.

No problems with it? Sure probably not initially and when it kills your air conditioner they will just tell you it died of old age. How nice of them?

How does it kill your air conditioner: Poor oil return to the compressor.

If you want to kill your air conditioner but good... go for it.

You have two choices: You should fix the refrigerant leak and recharge with virgin R22.

OR

Upgrade the equipment to work with R410a.

Either of these options require there to be no leaks, or your wallet will get drained repeatedly.

If you just keep recharging the unit with MO99 (R438a) it will kill your compressor. How long it will take? A day, a week, a month, a year. (most likely when it's hot outside.)

Oil return for a compressor is critical and running a compressor low on refrigerant isn't helping your situation.

If you were to use a different refrigerant in an R22 system, the new refrigerant would have to be retrofitted. R438A offers similar cooling performances and energy efficiency as R22, so theoretically, the system should work fine for the time being. However, when retrofitting a unit, there is a high potential for leakages as well as issues with other components of the unit.

If you are looking for a quick fix to get you through the summer, perhaps this is not the worst option. However, if you're hoping to get more life out of your unit, it would be best to recharge the unit with R22 refrigerant. It may also be worthwhile to consider a newer system at this time.